High-temperature brazing alloys



United States Patent v r 2,900,251 HIGH-TEMPERATURE BRAZING ALLOYSRobert Melvin Evans and Harry Edward Pattee, Columbus, Ohio, assignors,by mesne assignments, to The Trane Company, La Crosse, Wis., acorporation of Wisconsin V I -No Drawing. Application February 26, 1958Serial No. 717,558

11 Claims. (Cl. 75-170) This invention relates to brazing alloys whichare to be used at high temperatures where oxidation resistance andstrength are particularly important. More particularly, these newbrazing alloys are useful for brazing such metallic materials ashigh-alloy steels, stainless steels, nickel-chromium alloys, etc.

When joining metallic materials of construction for use at hightemperatures, especially if the metals being joined have very thinsections, considerable difiiculty is encountered in producing suitablearticles which are useful above 1000 F. Some brazing alloys, such asknown nickelbase alloys, are unsuitable for such applications becausesome of the constituents of the alloy diffuse into the grain boundariesof the parent metals, thus causing embrittlement and early failure inthe joint area. This condition is aggravated in those alloys having awide melting range. Other brazing alloys such as known silver-basealloys, which do not react with the parent metal during brazing are notsuitable for use above 1000 F. in ordinary hotair atmospheres becausethe interface between the brazing filler-metal alloy and the parentmetal rapidly oxidizes, thus rendering the joined article useless.

One object of this invention is to provide brazing fillermetal alloyswhich have oxidation resistance equal to, or better than, the metalbeing joined at temperatures above 1000 F. More importantly, the newbrazing alloysaccomplish the joining of the metal and permit use of thebrazing metal without serious impairment of the physical properties ofthe base metal at, or near, the braze.

In the assembling of complex structures made from stainless steel, theinventors have found that alloys with compositions such as given inTable I produce wellbonded assemblies which have excellent oxidationresistance at temperatures at least up to 1400 F. In addition, if thesealloys are properly used at temperatures slightly aove their meltingranges, very little attack of the stainless steel occurs in the form ofintergranular embrittlementor excessive alloying. Such improvements aremore noticeable in structures utilizing the thinner sections of metal,such as stainless steel of 0.005-inch thickness or thinner.

Table 1 Composition, weight percent Alloy Number Melting Range, F.Nickel Tin Silicon Palladium These alloys may be made by anyconventional method and preferably by a method which permits subsequentdisintegration into the powder form in which they are used. A preferredmethod of making the powdered alloy involves melting of the essentiallypure metal constituents 2,900,251 Patented Aug. 18,

in the following order: nickel and palladium first, followed by theaddition of the othermore easily oxidized lower melting constituents ina graphite or clay-graphite crucible. After melting in an inductionfurnace and stirring quickly, the molten alloy is poured into a highpres sure water jet and the resultant disintegrated metal is caught in atank along with the water. After drying and screening, the brazing,alloy is ready for use. The particular mesh sizes of the disintegratedbrazing alloy may be varied by, suitable selection of the disintegrationprocess and may be selected according to the particular application to.which the brazing alloy is applied.

These new alloys may be applied to-the area to be joined before actualbrazing by any conventional means. Some of these methods are painting,spraying, dipping, or extrusion. In each of these methods, the powderedalloy is mixed with, or suspended in,'a suitable carrier, such as anorganic solvent, or a synthetic rubber, or other carriers well known inthe art. The properties of the carriers must be such that they do notinterfere with the brazing operation. Brazing of metal preferably shouldbe done in a highly reducing atmosphere such as dry hydrogen, or in avacuum, but the brazing of heavy sections of metal may be accomplishedin a highly protec tive atmosphere, if desired.

A specific example of the results obtained when Alloy No. 24, Table 1,was used to join 0.003-inch A.I.S.I. type 347 Stainless Steel to0.005-inch A.I.S.I. Type 347 Stainless Steel illustrates the utility andadvantages of our invention. The alloy was mixed with a cement carriercomprising an acrylic ester resin solution, such as an Acryloid resinsolution of Rohm & Haas Company, made for high-temperature brazingoperations, to form a paste. The paste was then applied to the jointarea and the assembly was brazed in dry hydrogen at 2030 F. for 5minutes. Metallographic examination of a first part indicated noembrittling intergranular penetration of the stainless steel and verylittle interaction between the brazing alloy and the stainless steel.This improvement over known brazing alloys was noted even though thebrazing temperature was about F. above the preferred temperature forthis alloy. A second part of the same sample was exposed to. a movingair stream at 1300 F.

for 400 hours and again examined metallographically.

The brazed joint was intact showing oxidation resistance at least equalto the stainless steel parent metal.

Each of the alloys in Table 1 were utilized in a manner similar to theaforesaid Alloy No. 24 to braze metallic materials. Similar advantagesand improvements were nixed in the use of these other alloys embodied inTab e 1.

In making these new brazing alloys, it is within the scope of theinvention that the nickel content may be varied from 30 to 60 percent,the tin content from 20 to 45 percent, the palladium content from 10 to30 percent, and the silicon content from4 to 8 percent. It is alsowithin the scope of the invention that the nickel content may be variedfrom 45 to 5 8 percent, the tin content from 20 to 30 percent, thepalladium content from 10 to 30 percent, and the silicon content from 5to 7 percent. It is further within the scope of the invention that thenickel content may be varied from 45 to 49 percent, the tin content from20 to 30 percent, the silicon content from 5 to 7 percent, and thepalladium content from 20 to 30 percent. Additionally, it is within thescope of the invention to vary the nickel content from 51 to 58 percent,the tin content from 24 to 27 percent, the palladium content 10 to 20percent, and to maintain the silicon content at about 5 percent. Otherconventional alloying elements may be present in the alloys in minoramounts, provided the major elements composing the brazing alloy arewithin the ranges given. The preferred compositions among those given inTable 1 are Alloys No. 19,

No. 24, and No. 31.

What We claim:

, 1. An alloy for brazing for use at high temperatures consistingessentially of 30 to 60 percent nickel, 20 to 45 percent tin, 10 to 30percent p'alladium,4 to8 percent silicon. 7 v 1 2. An alloy for brazingfor use at high temperatures consisting essentially of 30 to 58 percentnickel, 20 to 45 percent tin, 10 to 30 percent palladium, 5 to 7 percentsilicon. v p

3. An alloy for brazing for use at high'ternperatures consistingessentially of 45 to 58 percent nickel, 2( to' 30 percent tin, 10 to 30percent palladium, 5 to 7 percent silicon. I I

4. An alloy for brazing consisting essentially of about 30 percentnickel, about 45 percent tin, aboutS percent silicon, about 20 percentpalladium.

6. An alloy for brazing consisting essentially of 51 to 58 percentnickel, 24 to 27 percent tin, about 5 percent silicon, 1 to 20 percentpalladium.

7. An alloy for brazing consisting essentially of about 8 percentnickel, about 27 percent tin, about 5 percent silicon, about 10 percentpalladium.

8. An alloy for brazing consisting essentially of about 51 percentnickel, about 24 percent tin, about 5 percent silicon, about percentpalladium. 9. An alloy for brazing consisting essentially of about 45percent nickel, about percent tin, about 5 percent silicon, about 20percent palladium.

10. An alloy for brazing consisting essentially of about 4 49 percentnickel, 24 percent tin, about 7 percent silicon,

about 20 percent palladium.

11. An alloy for brazing consisting essentially of about percent nickel,about 20 percent tin, about 5 percent silicon, about 30 percentpalladium.

5. An alloy for brazing consisting essentially of 45 to i 49 percentnickel, 20 to 30 percent tin, 5 to 7 percent silicon, 20 to 30 percentpalladium.

No references cited.

1. AN ALLOY FOR BRAZING FOR USE AT HIGH TEMPERATURES CONSISTINGESSENTIALLY OF 30 TO 60 PERCENT NICKLE, 20 TO 45 PERCENT TIN, 10 TO 30PERCENT PALLADIUM, 4 TO 8 PERCENT SILICON.